• Journal of Convergence for Information Technology
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• v.7 no.3
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• pp.97-103
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• 2017

In this paper, we aim to investigate the generalization of ZRC codes by performing performance analysis on various coding rates and channel conditions of Zero Reduction Code (ZRC) for dimming control in VLC system. Simulation results show that the ZRC codes with relatively high coding rate achieve the enhanced BER performance as the RMS (Root Mean Square) delay spread value increases in the NLOS channelse. Therefore, it is expected that the designing of the dimming control technology using ZRC in the future visible light communication system will help to determine the coding rate according to the channel state through the analysis result in this study.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.4
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• pp.292-299
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• 2012

The line-of-sight(LOS) rate is estimated using Kalman filter in Radio-Frequency(RF) seeker. For the two axis gimbaled seeker, proper system modeling is considered and the basic filter structure is set up. The main issue for Kalman filter is choosing the proper process and measurement noise. For the measurement process, the signal to noise ratio(SNR) and other components are introduced. To cope with the eclipse problem or other abnormal seeker status, the pseudo input signal concept is proposed. By conditioning abnormal signals, the LOS rate estimation performance is increased. The process noise is also an important factor in the propagation phase. The analytical approach on a process noise component is performed and a reliable region for the filter is calculated based on the eigenvalue analysis. Some numerical simulations are performed to check the validity of suggested algorithm.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.12A
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• pp.1883-1890
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• 1999

Wireless communication in an urban area, the accurate prediction of wave propagation characteristics are very important to determine communication service areas, select optimal base-stations, and design cells, etc. The CCIR model is a propagation prediction model using a shadowing by the buildings in an urban area. This model represent the shadowing rate by the means of the effect of shadowing between base-station and mobile unit in a shaped linear plane. But, This one occurred a lot of prediction error because it did not consider that density area by the buildings and terrain configurations by the hill and mountain on Line-Of-Sight. In this thesis, an improved propagation prediction model is proposed to reduce prediction error. We presents a new equation, which is using the SAS. This equation is associated with the shadow height by the buildings that considers the topology and the number of blocks that can affect the building shadow in the Line-Of-Sight. We measure the received electrical field level of base-station that high density area, medium density area, and low density area, and then compare and analysis the result to prediction of CCIR model and proposed model. The result compared with the measurement, the proposed model has the improvement of 9.71dB in a high density area, 9.66dB in a medium density area, and 4.02dB in a low density area better than the CCIR model. The result compared with the measurement, the proposed model has the improvement of 9.71dB in a high density area, 9.66dB in a medium density area, and 4.02dB in a low density area better than the CCIR model.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.7
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• pp.1397-1404
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• 2015

Recently, high data rate transmission is required in maritime communication. In this paper, we consider multiple input multiple output (MIMO) spatial multiplexing (SM). However, the performance of SM is severly degraded due to spatial channel correlation and line-of-sight (LOS) component. In the maritime communication, the MIMO channel correlation and LOS are critical due to the lack of scatteres around the transmitter and/or the receiver. When the feedback of channel information is available, precoding can enhance the error performance by exploiting the channel information. However, it is difficult to derive closed-form solution considering both the correlation and LOS. In this paper, we present open-loop precoding-based spatial multiplexing transmission method by showing that the effect of performance for the correlation and LOS. It is shown that the open-loop precoding can mitigate the performance degradation due to the LOS as well as the correlation. Consequently, we expect that the proposed open-loop precoding can be adopted to the maritime communication system.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.4
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• pp.1590-1610
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• 2016

The challenge of penetrating obstacles along with impact from weak multipath effects makes 60GHz signal very difficult to be transmitted in non-line of sight (NLOS) channel. So 60GHz system is vulnerable to obstructions and thus likely results in link interruption. While the application of cooperative technology to solve link blockage problemin 60GHz system should consider the characteristic of directional transmission for 60GHz signal. Therefore in this paper a system is proposed to solve the link blockage problem in 60GHz NLOS communication environment based on the concept of cooperation and also the beamforming technology, which is the basis of directional transmission for 60GHz communication system. The process of anti-blockage solution with cooperative communication is presented in detail, and the fast switching and recovery schemes are well designed. The theoretical values of symbol error rate (SER) using decode and forward (DF) cooperation and amplify and forward (AF) cooperation are presented respectively when the common channel interference exists. Simulation results demonstrate that the performance based on DF cooperation is better than the performance based on AF cooperation when directional transmission is used.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.220-220
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• 1999

In plasma source ion implantation, the target is immersed in the plasma and repetitively biased by negative high voltage pulses to implant the extracted ions from plasma into the surface of the target material. In this way, the problems of line-of-sight implantation in ion-beam ion implantation technique can be effectively solved. In addition, the high dose rate and simplicity of the equipment enable the ion implantation a commercially affordable process. In this work, plasma source ion implantation technique was used to improve the wear resistance of Co-cemented WC. which has been extensively used for high speed tools. Nitrogen and carbon ions were implanted using the pulse bias of -602kV, 25 sec and at various implantation conditions. The implanted samples were examined using scanning Auger electron spectroscopy and XPS to investigate the depth distributions of implanted ions and to reveal the chemical state change due to the ion implantation. The implanted ions were found to have penetrated to the depth of 3000$\AA$. The wear resistance of the implanted samples was measured using pin-on-disc wear tester and the wear tracks were examined with alpha-step profilometer.

• Proceedings of the KSRS Conference
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• 2004.10a
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• pp.594-597
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• 2004

The ground subsidence that occurred in an abandoned coal mining area, Gaeun, Korea, was observed by using 25 JERS-1 SAR interferograms from November 1992 to October 1998. We estimated the subsidence on a subset of image pixels corresponding to point-wise permanent scatters (PSs) by exploiting a long temporal series of interferometric phases. The results were compared it with a distribution map of in situ examined crack level. PSs were identified by means of amplitude dispersion index and coherence of the interferograms. The measured subsidence rate represented the average velocity in a period of image acquisition and excluded complex nonlinear displacements such as an abrupt collapse. The mean line-of-sight velocity in the study area is 0.19cm/yr and an r.m.s. error is 0.18cm/yr. The center of the abandoned Gaeun coal mine (0.49cm/yr) and the area near to the Gaeun station (1.66cm/yr) were observed as most rapidly subsiding areas.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.11
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• pp.1-10
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• 2007

In this paper, we proposed channel estimation scheme for LR-UWB system which has low data rate for WPAN in IEEE 802.15.4a. At the transmitter, we proposed dynamic power level allocation depends on channel condition in specific period when we modulate signal. We use two orthogonal code to estimate channel at once. It can estimate channel more accurately by using two code which shows good correlation characteristic then it can estimate more accurately by spreading gain. Using estimated channel condition, we synchronize symbol timing of transmitted signal. Then determined power allocation scheme and channel information is transmitted to transmiter side. Finally, using these information, transmiter side change the power level of repeated pulse to adopt to channel condition. Simulation is performed under S-V channel for LR-WPAN in IEEE 802.15.4a and we compare the performance with a different type of receiver type. We use coherent and non-coherent method at the receiver. Simulation result shows us at the NLOS channal performance evaluation is greater than that of LOS channel and the result is independent of receiver type. In the NLOS channel, as the signal delay spreading is big, performance evaluation is also increased.

• Journal of Positioning, Navigation, and Timing
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• v.11 no.1
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• pp.11-21
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• 2022

Fast Fourier transform (FFT)-based parallel acquisition techniques with reduced computational complexity have been widely used for the acquisition of binary phase shift keying (BPSK) global positioning system (GPS) signals. In this paper, we propose a low computational FFT-based fine acquisition technique, for binary offset carrier (BOC) modulated BPSK signals, that depending on the subcarrier-to-code chip rate ratio (SCR) selectively utilizes the computationally efficient frequency-domain realization of the BPSK-like technique and two-dimensional compressed correlator (BOC-TDCC) technique in the first stage in order to achieve a fast coarse acquisition and accomplishes a fine acquisition in the second stage. It is analyzed and demonstrated that the proposed technique requires much smaller mean fine acquisition computation (MFAC) than the conventional FFT-based BOC acquisition techniques. The proposed technique is one of the first techniques that achieves a fast FFT-based fine acquisition of BOC signals with a slight loss of detection probability. Therefore, the proposed technique is beneficial for the receivers to make a quick position fix when there are plenty of strong (i.e., line-of-sight) GNSS satellites to be searched.

• Journal of Institute of Control, Robotics and Systems
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• v.15 no.5
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• pp.496-504
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• 2009

This paper presents a recognition performance of VOR (Vestibular-Ocular Reflex) based vision tracking system for mobile robot. The VOR is a reflex eye movement which, during head movements, produces an eye movement in the direction opposite to the head movement, thus maintaining the image of interested objects placed on the center of retina. We applied this physiological concept to the vision tracking system for high recognition performance in mobile environments. The proposed method was implemented in a vision tracking system consisting of a motion sensor module and an actuation module with vision sensor. We tested the developed system on an x/y stage and a rate table for linear motion and angular motion, respectively. The experimental results show that the recognition rates of the VOR-based method are three times more than non-VOR conventional vision system, which is mainly due to the fact that VOR-based vision tracking system has the line of sight of vision system to be fixed to the object, eventually reducing the blurring effect of images under the dynamic environment. It suggests that the VOR concept proposed in this paper can be applied efficiently to the vision tracking system for mobile robot.